1. Field of the Invention
The present invention relates to dental equipment and more particularly relates to a method and apparatus for forming metal copings and matrices.
2. General Background and Prior Art
In forming crowns, a new popular technique is the McClean-Sced technique. In this technique, aluminous porcelain is fused to thin platinum foil copings. With the McClean-Sced process, the copings can be of a substantially reduced thickness on the order of one to two thousandths (0.025mm or 0.05mm) of an inch. Thus, the cost of metal for the individual metal-ceramic crowns is reduced. The McClean-Sced process relies on the electro-deposition of a very thin coating of pure tin on the surface of the foil coping. Subsequent oxidation of this tin-coated platinum foil causes the tin to alloy and oxidize on the platinum surface. The continuous film of tin oxide provides a perfect medium for porcelain bonding. The electro-deposition process allows automatic timing of the coating process and is also used to degrease the surface of the matrix before applying the tin. The accuracy of the timing apparatus ensures that only a very thin coat of tin is applied and this should not be greater than 0.5 to 1 mincons thick.
The tooth preparation should conform to the standard aluminous porcelain jacket crown preparation.
Before the present invention, the foil has been applied to the die and conformed thereto by a procedure using a "tinner's joint."
The use of the "tinner's joint" provides an undesireable fold in the foil sheet which thereafter causes problems when the porcelain is to be added to the coping in the standard jacket crown process.
In the prior art method of forming the matrices or copings, which method uses the "tinner's joint," the foil is made to conform to the shape of the tooth die by means of manual burnishing. This procedure is time consuming and also undesireable because of the aforementioned problem of the "fold" produced by the "tinner's joint" which thereafter leaves a thickened area to which the porcelain is not as well adhered.